This invention relates to a universal joint with an improved fail-safe lubrication system.
Universal joints have found wide application in automotive, agricultural, aircraft, industrial and instrument applications to couple two rotary shafts that have an angular misalignment. A particularly common type of constant velocity universal joint is the double Hooke's joint. A double Hooke's joint typically comprises a double inner housing, a pair of outer yokes, a pair of cross-links with each cross-link pivotally connecting one of the outer yokes to one of the ends of the double inner housing, and a centering apparatus for connecting the two outer yokes to one another. The drive shaft is connected to one of the outer yokes and the driven shaft is connected to the other outer yoke. The centering apparatus operates to equalize the angles between the drive shaft, the driven shaft, and the axis of the double inner housing to provide a constant velocity ratio between the drive and the driven shaft.
Continual metal-to-metal sliding contact in the centering apparatus has posed a problem in prior universal joints. Lubrication has been the basic solution, but it has been difficult to insure easy application of the lubricant to the proper place in the centering apparatus and that the lubricant stay there during operation of the joint. Under operation, centrifugal forces act on the lubricant which tend to throw the lubricant radially outward. Normally, lubrication fittings have a one-way check valve which keeps the lubricant from being thrown outside of the centering apparatus. However, if the lubrication fitting malfunctions, works loose, is removed, or is broken off, the lubricant could have been lost in prior universal joint centering apparatuses. This resulted in running the centering apparatus dry and consequent accelerated wear of the centering apparatus.